Engines may include crankcase ventilation systems to vent gasses out of the crankcase, which may reduce degradation of engine components housed within the crankcase. A typical crankcase ventilation system couples the crankcase to intake via a crankcase ventilation tube (fresh air hose). The ventilation tube may be monitored to identify degradation that limits crankcase ventilation. For example, if the ventilation tube is disconnected at either the intake side or the crankcase side, airflow through the canister may be limited.
A pressure sensor within the crankcase ventilation tube or the crankcase itself may be utilized to diagnose degradation within the crankcase ventilation system. However, merely indicating a crankcase pressure may be insufficient to determine the location of the degradation, yielding a more time consuming and costly repair. Other attempts to discern crankcase ventilation breaches include adding additional sensors, or performing diagnostic tests during when specific canister pressure profiles are expected. One example approach is shown by Rollinger et al. in U.S. 2014/0081549. Therein, crankcase-side degradation of the fresh air tube is determined at engine crank when a pressure dip in the crankcase is expected, and intake-side degradation of the fresh air tube is determined when intake manifold airflow is increasing and crankcase pressure is expected to be decreasing.
However, the inventors herein have recognized potential issues with such systems. As one example, crankcase pressure may change due to reasons unrelated to intake air flow. For example, a mechanical vacuum pump (e.g., brake booster pump) may be deposed at least partially within the crankcase to ensure the pump is lubricated. However, if the vacuum pump exhausts into the crankcase, the crankcase pressure may change, yielding a crankcase pressure profile similar to those for a degraded crankcase ventilation tube. This may result in false-fail results of crankcase ventilation integrity tests. If the vacuum pump exhausts directly to intake, it may represent an additional source of unmetered fuel entering intake, which may lead to an increase in engine stalls.
In one example, these issues may be addressed by a system for an engine, the system comprising a vacuum pump at least partially deposed within an engine crankcase, and a fuel vapor canister coupled to an exhaust conduit of the vacuum pump via a one-way valve. By coupling the vacuum pump exhaust to the fuel vapor canister, unmetered fuel vapor flow to the engine intake may be reduced, thus decreasing engine stall events. Further, crankcase pressure may more accurately represent airflow through the crankcase via a crankcase ventilation system, thereby improving the accuracy of crankcase ventilation diagnostics. In this way, false-failures of crankcase ventilation integrity tests may be reduced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.